Includable vs Includible

In many contexts, authors often interchange these terms; however, they are different, and their nuance can have a big impact, especially in a legal sense or context.

https://thecontentauthority.com/blog/includable-vs-includible

Looping back on the IRC 3402 posts last week, we can see that the term “are includible” is used in the language of the regulation.

What exactly does this mean? In a legal context, the linked site states the following:

It appears that the Treasury’s deliberate usage of “includIBLE” suggests that they are quite aware that “other amounts” which are “TREATED as wages” for purposes of being “includIBLE” in gross income are not necessarily REQUIRED to be included in one’s gross income EVEN IF that person actually filled out a W-4 without duress.